Process for tanning with iron salts



I To all-whom it may concern:

M ran N o nc.

o'rro Romvr, or DARMSTADT, GERMANY, ASSIGNOR, av MESNE AssmNMEN'rs, 'ro THE CHEMICAL FOUNDATION, me, A CORPORATION or nnLAwnnn.

rnocnss ron TANNING WITH IRO SALTS.

No Drawing.

Be it known that I, OTIO RoHM, a subject of the King of Wurttemberg, residing at No.

4.6 Weiterstadterstrasse, 'in the city oh Darmstadt, Grand Duchy of Hessia, German Empire, have invented an Improvement in Processes for Tanning with Iron Salts; and I do hereby declare that thefollowing is a full, clear, and exact description of the same. I

In tanning with the usual iron salts, such as ferric chloride, or sulphate of iron, it has been noticed that the'leather,'- if, after it has been tanned, it is treated with water, will allow the tanning principle to; issue from the grain. This appearance is known as bleeding. As a consequencethe grain be- -"comes defective, \and the leather, being insufiiciently tanned, can become hard. With the object of preventing this bleeding,-the leather, after it has been allowed to remain in a moist condition for several days, or without such treatment, can be neutralized with carbonic acid, or boric acid salts, or alkalies, or-alkaline"earths, but this is a diflicult task. It is particularly necessary to take care not to carry the neutralization too far, because otherwise the grain will become brittle. Only by exercising the greatest care is it possible to entirely avoid this mistake. v

Now it has been found that thisbleeding of the leather can be easily prevented, if,

instead of one of the usual inorganic salts,

formate of iron alone, or together with inorganic iron salts is used for the tanning process.

1 The solution can be either acid or basic.

' Leather produced in this Way can be immediately treated with water, that is, without being ffirst stored, and without being neutralized, and doesnot lose, its tanning. For example 100 parts of depilated skins I are treated with 150 partsof water, 3 parts of common salt and '2 parts of formic acid and then with 30 parts basic' formate o I iron, with gradual strengthening.

Or 100 parts of depilated skins aretreated with 150 parts of ,water, 30 parts of common salt and 2 parts of hydrochloric acid and Specification of Letters Patent. Patented A110, 15, 1922,

Appli cation filed June 13, 1917. Serial No. 174,643.

then with 15 parts of basic chloride of iron and 15 parts of basic formate of iron, with gradual strengthening.

Further it has beenfound that the bleeding is 'also'prevented if the moist leather taken out of the tanning liquor is treated with the solution of a salt of lower fatty acids. Of special advantage, for example, are the calcium salts. of formic or acetic acid. In'this case no' loss of tanning principleoccurs on washing the leather, and a previous neutralization is unnecessary.

According to this process, for example, 100 parts of leather tanned with basic solution. of ferric chloride are agitated for half an hour in 200 parts ofwaterand 8 parts of formate of calcium, whereafter it ,is washed with water, greased, dyed and trimmed.

It. has indeedbeen proposed to treat ferro leather, after it. has been tanned with solutions of neutral salts of alkalies, such as sodium sulphate and sodium chloride. The salts of fatty acids however are much superior to such an organic sodium salts.

What I claim and desire to secure by Letters Patent of the United States is:

1. Theprocess of tanning consisting in subjecting the leather to the action of iron salts, thentreating the same with a neutralizing agent without rendering the grain of the leather brittle, and finally subjecting the leather thus treated to the action of ide and an-acid, and then further treating the skins with basic chloride of iron and basic formate of iron.

- 4. The process of tanning leather consist- I ing in subjecting the skins to the action of a solution of an iron salt, alower fatty acid and an organic iron salt.

' QTTO ROI-1M. 

